[2] The county was officially organized on August 21, 1813, and was named in honor of George Washington, the first President of the United States.

[3] The French explorers Renault and La Motte entered the area of present-day Potosi in 1722–23.

However, no permanent settlements were made until 1763, when François Breton settled near Potosi and began to operate a mine bearing his name.

Washington County is divided into three legislative districts in the Missouri House of Representatives.

Smith won a special election on Tuesday, June 4, 2013, to finish out the remaining term of U.S. Representative Jo Ann Emerson (R-Cape Girardeau).

Emerson announced her resignation a month after being reelected with over 70 percent of the vote in the district.

Like most rural areas throughout Missouri, voters in Washington County generally adhere to socially and culturally conservative principles but are more moderate or populist on economic issues, typical of the Dixiecrat philosophy.

The proposition strongly passed every single county in Missouri with 75.94 percent voting in favor as the minimum wage was increased to $6.50 an hour in the state.

In 2018, Washington County rejected Proposition A which would have made Missouri a right-to-work state with 82.1 percent of the vote.

Among adults 25 years of age and older in Washington County, 62.5% possess a high school diploma or higher, while 7.5% hold a bachelor's degree or higher as their highest educational attainment.

Major fire departments in the county include those of Potosi, Richwoods, Irondale, Belgrade, and Caledonia.